1. Field of the Invention
This invention relates to a method and system for automatically adjusting the color balance of a color TV camera.
2. Description of the Related Art
An automatic color-balance setup system for automatically adjusting the differences of the circuit characteristics of the three channels, R, G and B, of a color TV camera is disclosed in, for example, JP-B-50-19410. The cited system uses a reference chart board on which specific patterns representing a white level, a black level and a gray level are drawn to exhibit a guaranteed color balance among them. The manner of automatic color-balance adjustment in the proposed system has been such that the reference chart board is imaged by the color TV camera, and the camera output signal representing the image is displayed on a monitor TV set. Thus, in the proposed system, it has been required to adjust the position of the reference chart board relative to the TV camera, so that the pattern of the white level, that of the black level and that of the gray level can be accurately displayed at the specific positions respectively on the screen of the monitor TV set.
FIG. 1 shows schematically the arrangement of a conventional system. The structure and operation of the conventional system will now be described by reference to FIG. 1. Referring to FIG. 1, white, black and gray patterns for generating signals of reference levels to be used for the purpose of automatic setup are drawn on a reference chart board 1. The patterns drawn on the chart board 1 are imaged by a color TV camera 2, and the image signal is displayed on the screen of a monitor 3. The color balance is adjusted by an automatic setup device 2a. In this case, the locations where the signals of white, black and gray levels respectively are derived on the screen are determined beforehand, and the data of the individual signals corresponding to those locations are used to execute the automatic setup. In the case of the conventional system shown in FIG. 1, the reference numerals 7, 8 and 9 designate a white level measurement region, a black level measurement region and a gray level measurement region respectively on the screen of the monitor 3. Therefore, in order that the automatic setup can be accurately executed, it is necessary to adjust the relative positions of the TV camera 2 and the reference chart board 1, so that the white level measurement region 7 is to be included in the range of a white level generation pattern 4, the black level measurement region 8 is to included in the range of a black level generation pattern 5, and the gray level measurement region 9 is to be included in the range of a gray level generation pattern 6. This positioning of the reference chart board 1 relative to the TV camera 2 has been executed hitherto while a user is observing the screen of the monitor 3 by user's eyes.
Therefore, the conventional system has had the following three problems (1) to (3):
(1) The positioning of the reference chart board 1 relative to the TV camera 2 requires a considerably long time.
(2) Because the system is based on specifying the measurement regions of the individual levels, a reference chart board of a specific type can only be used.
(3) When at least one pattern located at the position corresponding to one of the individual level measurement regions of the reference chart board 1 is partly fouled or damaged, the reference chart board 1 cannot be used for the purpose of automatic setup anymore.